I'd like to see the feature like vBulletin where you can create attachment extension and give permissions based on groups (which groups are allowed to use and the file size limits etc)
Permission-based upload constraints for attachments, avatars, profile banners Add-on features: Permission-based upload constraints for: Attachments: Max count per message, max size, width and height Node-based permissions for posts (Forum...
xenforo.com
There is no extension-based permissions (and seems permissions system is not good for it), but i can add option with list of groups and allowed file extensions if someone really interested in.